1. Field of the Invention
The present invention relates to nonreciprocal circuit devices and communication apparatuses using the devices. In particular, the present invention relates to a nonreciprocal circuit device, such as an isolator or a circulator, which is used in a microwave band, and to a communication apparatus using the device.
2. Description of the Related Art
FIGS. 10, 11, 12A and 12B show a lumped-constant-type isolator (nonreciprocal circuit device) for use in a mobile communication apparatus, such as a cellular phone, including a resin case 1, a center-electrode assembly 10 including a ferrite 11 and center electrodes 12a, 12b, and 12c, a permanent magnet 15, a resistor 16, matching capacitors 17, and metallic cases 18 and 19, as shown in FIGS. 10 and 11. In FIG. 12A, the resin case 1 is provided with external input-output terminals 5 and external grounding terminals 6 as metallic insert parts (a lead frame) being embedded at both sides of the bottom of the resin case 1 when the resin case 1 is molded.
Each of the external terminals 5 or 6 of the reciprocal circuit device projects from the bottom of the resin case 1 by a projection amount Y (see FIG. 12B). The projection amount Y tends to become smaller as the nonreciprocal circuit device is reduced in size and becomes low-profile. In recent years, the projection amount Y has been on the order of 0 to 100 xcexcm.
As the projection amount Y is reduced, as described above, a mismatch between the lead frame and a mold causes a phenomenon in that the resin partly covers the external terminals. In FIG. 12A, excess resin 1a is seen partially covering the external input-output terminal 5 disposed at the right side.
When the projection amount Y is large, the excess resin 1a does not reach the bottom face of the external input-output terminal 5 and does not affect mounting of the nonreciprocal circuit device. However, when the projection amount Y is small, the excess resin 1a reaches the bottom face of the external input-output terminal 5, thereby causing a harmful effect on the mounting of the device. That is, when mounting, the external input-output terminal 5 and an electrode formed on the circuit board cannot be soldered to each other, whereby electrical connection becomes open, or even when these can be soldered to each other, the strength of connection is not sufficient, thereby reducing reliability. Such a problem can be solved by increasing the projection amount Y. However, it is not practical to increase the projection amount Y because it is desirable for the device to be reduced in size and also to be low-profile.
Also, the resin flows into the notches that are provided for cutting the device from a lead frame, the notches being formed in connecting parts of the lead frame, which causes a problem in which burrs of the resin are produced when the lead frame is cut at the connecting parts, whereby the device cannot be reliably mounted.
It is an object of the present invention to provide a nonreciprocal circuit device and a communication apparatus using the nonreciprocal circuit device in which resin can be prevented from being applied to bottom faces of external terminals during insert molding and which can be reduced in size and be low-profile, whereby the nonreciprocal circuit device can be reliably mounted.
It is another object of the present invention to provide a nonreciprocal circuit device and a communication apparatus using the nonreciprocal circuit device in which resin can be prevented from flowing into notches formed in connecting parts of a lead frame during insert molding, whereby the nonreciprocal circuit device can be reliably mounted.
To these ends, according to an aspect of the present invention, a nonreciprocal circuit device comprises a resin case; and external terminals insert-molded with the resin case so as to project from the resin case when the resin case is molded. The resin case is provided with concavities each formed in a bottom face of the resin case and in the vicinity of a position from which each external terminal projects.
With this arrangement, when the external terminals of the nonreciprocal circuit device are insert-molded with the resin case and excess resin is supplied, the oversupplied resin is absorbed by the concavities formed in the bottom face of the resin case and is not applied to the bottom faces of the external terminals. Therefore, reliable soldering can be performed so as to have sufficient joint strength even when the projection amount of the external terminals is reduced so that the size of the nonreciprocal circuit device is reduced and becomes low-profile, and solder fillets can be formed in excellent shapes. Moreover, since the external terminals and electrodes of a mounting substrate can be reliably brought into contact with each other, insertion loss can be reduced. When the external terminals and the electrodes of the mounting substrate are not brought into contact with each other, they come into contact with each other only via solder which has high resistance, thereby increasing the insertion loss.
According to another aspect of the present invention, a nonreciprocal circuit device comprises a resin case; and external terminals which are formed with a lead frame and are insert-molded with the resin case when the resin case is molded. The resin case is provided with concavities each formed in a bottom face of the resin case, and in the vicinity of a notch formed in each of connecting parts which are formed with the lead frame and are insert-molded with the resin case when the resin case is molded.
When the connecting parts of the lead frame of the nonreciprocal circuit device according to the present invention are insert-molded with the resin case, the resin flowing toward the notches formed in the connecting parts is absorbed by the concavities which are formed in the bottom face of the resin case, and does not flow into the notches, whereby burrs of the resin are prevented from being produced when the connecting parts are cut at the notches.
Each of the concavities, which are formed in the bottom face of the resin case, preferably has a depth of 0.01 to 0.1 millimeters. When the concavities are excessively deep, the joint strength between the resin case and the external terminals or connecting parts is reduced. When the concavities are excessively shallow, the resin flowing toward the notches cannot be sufficiently absorbed by the concavities.
A material for the resin case preferably comprises one of liquid crystal polymer, polyphenylene sulfide, and polyetheretherketone, which are heat-resistive and are low-loss materials. The material for the external terminals may comprise as a major component one of iron, brass, and phosphor bronze, which are easily bent.
According to another aspect of the present invention, a communication apparatus comprises the above-described nonreciprocal circuit device.
The nonreciprocal circuit device according to the present invention is provided with concavities each formed in the vicinity of the external terminals projecting from the bottom of the resin case or in the vicinity of the notches formed in the connecting parts of the lead frame. Therefore, the resin is absorbed by the concavities when the resin case is molded, whereby the resin does not cover the bottom faces of the external terminals or does not flow into the notches of the connecting parts.
Therefore, reliable soldering of the external terminals having sufficient joint strength can be performed without increasing the projection amount of the external terminals, thereby permitting a reduction of size and a low-profile feature. The nonreciprocal circuit device can be reliably mounted without producing burrs of the resin when the connecting parts of the lead frame are cut at the notches.
A reliable communication apparatus is obtainable by being provided with the nonreciprocal circuit device having the above advantages.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.